Piston for internal combustion engines



April 4, 1939. W. HARPERq JR l PISTON FOR INTERNAL GOMBUSIION ENGINES Filed April 29, 1936 Patented Apr. 4, l@

PHSTN FOR INTERNAL COMBUSTION ENGWES William Harper, Jr., Port Washington, N. Y., as-

signor to H. B. Motor Corporation, New York,

N. Y., a corporation Application April 29,

' 7 Claims.

This invention relates to pistons for internal combustion engines and aims to increase the power output of such engines, and particularly the power-to-weight ratio of airplane engines.

I have found that a limiting factor on the sustained power output of internal combustion engines lies in the danger of overheating the forward end of the piston. The heat absorbed by the forward end of the piston from the burning gases must be dissipated from the piston wall to the cylinder wall in order to avoid injurious overheating of the forward end of the piston. When a comparatively thin-walled,'light piston is used, the conduction of heat through the metal of the piston is not suciently rapid to prevent local overheating of the front end of the piston when the maximum power output isbeing obtained from the'engine. I have overcome this dilculty by providing a piston with special and highly eective means for conducting heat from the front end of the piston to the cylinder wall.

A piston embodying my invention has in its Wall sealed pockets of irregular cross-section extending from the front end of the piston to the portions of the side wall of the piston which carry Athe piston rings. These pockets are partially filled with a heat-transfer material which provides an elcient means for transferring heat from the front end of the piston to the part of the piston carrying the piston rings from which the heat is readily conducted to the cylinder wall,

and serves to stabilize the temperature of the piston.

Other features of the invention will appear bodying my invention which are shown as illustrative examples in the accompanying drawing, in which Figs. 1, 2 and 3 show the application of the invention to a special type of piston utilized in the two-cycle aviation engine described in my Patent 2,041,709, May 26, 1936, and Figs. 4, and 6 show the application of the invention to an ordinary type of piston.

Fig. l is a front View of the special piston with parts broken away; Fig. 2 is an axial section on a plane perpendicular to the Wrist pin; and Fig. 3 is an axial section on the plane containing the axis of the wrist pin.

Fig. 4 is a front View of an ordinary form of 50 piston; Fig. 5 is an axial section of this piston on a plane perpendicular to the wrist pin; and Fig. 6 is an axial section on the plane containing the axis of the wrist pin.

The special piston shown in Figs. 1, 2 and 3 has an outwardly projecting front wall I0 and a from a detailed description of the pistons emof New York 1936, Serial No. '76,906

(Cl. 12S-176) side wall or skirt II having a portion I2 containing grooves I3 for the piston rings, and an outer portion carrying internal bosses l5 for a wrist pin I6.

In the wall of the piston are formed two pockets 20 which extend from the front wall I0 down the portion I2 of the side wall and terminate at the bosses I5. The portions of the side wall containing the pockets 20 serve as strengthening ribs extending between the bosses I5 and the front wall I0. This structure adds to the strength of the piston without substantially increasing its weight. The pockets 20 are of irregular crosssection as shown in Figs. 1 and 2.

Bores 2| extending transversely through the bosses I5 provide access to the pockets 20. The bores 2l are threaded so that they may be closed and sealed by screw plugs 22 after the pockets 20 have been partially filled with a heat-transfer medium 23. The bore 24 for the wrist pin is formed in the bosses I5 after the screw plugs 22 have been inserted. The outer-end portions 22a of the plugs 22 form a convenient means for attaching auxiliary parts such as a baffle 25 and a set-screw 26 for the wrist pin IG.

As the heat-transfer medium 23, I use a substance which undergoes a change of state with absorption of latent heat at a temperature between 200 F. and 400 F.v and which does not deleteriously affect the metal of which the piston is made. I have found it desirable to use a substance whose fusing point is between 200 F. and 400 F. and whose boiling point is above 900 F. In an aluminum piston, I have found sulphur a satisfactory heat-transfer medium. In an iron piston, I preferv to use sodium nitrate or sodium nitrite, or a mixture of the two. A readily fusible metal, such as tin, may also be used. It is de- 'sirable to add to the heat-transfer medium, when it is placed in the pockets, a small percentage of a mild oxidizing agent, such as sodium permanganate. When the piston is heated, the oxidizing agent and such air as is contained in the pockets serves to form on the walls of the pockets a layer of an oxide of the metal of which the piston is made, and this layer tends to prevent'the absorption into the metal of the piston of the heattransfer agent.

Besides effecting transfer of heat in the manner described, the heat-transfer medium by absorbing and giving off latent heat tends to stabilize the temperature of the portion of the piston carrying the rings at about the temperature at which the heat-transfer medium changes its state. This stabilization of temperature facilitates maintaining an accurate tight t between the piston and the cylinder during the operation of the piston.

-In the use of the piston in an engine, the heattransfer medium 23 is fused (except in some cases .for a small portion close Ato the plugs 22) and serted in the grooves I3.

The piston shown in Figs. 4, and 6 is of an Aordinary form having a flat front Wall l0 and a side wall or skirt l I. In this case, the irregularly shaped pockets 20' extend from points near the center of the ilat front wall I0 to the portion I2' of the side wall containing the grooves I3 for the piston rings. The inner walls of the lower portions of the pockets 20' provide strengthen-A f; ing ribs between the front wall of the cylinder and the wrist p'in bosses, so that the construction adds to the strength of the piston without substantially increasing its Weight. As in the modication first described, the pockets are partially lled with heat-transfer medium 23' through bores 2|" in the wrist pin bosses I5', and these bores are closed by screw plugs 22. This construction results i`n effective cooling of the cen- 1 tral portion of the front wall of the piston and prevents overheating of the, front wall.

What I claim is:

l. A piston for internal combustion engines containing a plurality of sealed, spaced pockets each extending for a fraction of the circumference of the piston and in 'said pockets a heattransfer medium in a movable :duid form which is agitated by the movement of the piston, so that the metal stresses are reduced by maintaining the whole pistonstructure at a more uniform temperature.

2. A piston for internal combustion. engines having a front wall and a side wall, wrist pin bosses extending inwardly from the side wall of the piston, the walls of the piston containing pockets extending respectively from the vfront wall of the piston to one of said bosses and each boss containing a transverse bore communicating with its correspondingpocket, a heat-transfer medium partially nlling said pockets, and plugs in said transverse bores sealing said material in the pockets.

3. A piston for internal combustion engines having a front wall and a side wall. wrist pin bosses extending inwardly from the side wall of the piston, the wallsof the piston containing pockets of irregular cross-section extending respectively fromthe front .wall of the piston to one of saidbosses and each boss containing a transverse bore communicating with its corresponding pocket, a heat-transfer medium partially lling said pockets,` and plugs in said transverse bores sealing said material'inthe pockets.

4. A piston for internal combustion engines having a'front wall and alside wall, wrist pin bosses extending inwardly from the side wall of the piston, the walls of the piston containing pockets of irregular cross-section extending respectively from `the front Wall of the piston to one of said bosses and each of said bosses containing a threaded transverse bore communicating with its corresponding pocket, a heat-transfer medium partially lling said pockets, and threaded plugs screwed into said transverse bores and seal- `ing said material in the pockets.

5. A piston for internal combustion engines having a front Wall and a side wall, wrist pin bosses extending inwardly from the side wall of the piston, the walls of the piston containing pockets of irregular cross-section extending respectively from the front wall of the piston to vone of said bosses and each of said bosses containing a threadedv transverse bore communicating with its corresponding pocket, a heat-transfer medium partially filling said pockets, threaded plugs screwed into said transverse bores and sealing said material in the pockets, said bosses and said `plugs containing a bore for the recepn tion of the wrist pin.

6. A piston for internal combustion engines having a front wall and a side wall, wrist pin bosses extending inwardly from the sidel wall of the piston, strengthening ribs extending along the inner side wall from the bosses to the front wall of the piston, said ribs and the Walls of the piston containing pockets extending respectively from the front wall of the piston to one of said bosses and each of said bosses containing a transverse bore entering its correspondingpocket, a heat-transfer medium in said pockets, and plugs in said transverse bores sealing said material in the pockets.

7. A piston for internal combustion engines having a front wall and a side wall containing grooves for piston rings, wrist pin bossesv extending inwardly from the side wall of the piston be- .yond the piston ring grooves, strengthening ribs extending respectively along the side walls of the piston from each'of said bosses to the front wall of the piston, each of said ribs and the walls of the piston containing a pocket of irregular crosssection extending from the front wall of the piston to the portion of the side wall of the piston containing the piston ring grooves, and wrist pin bosses each containing a. threaded transverse bore entering its corresponding pocket, screw plugs'in said bores closing said pockets, said screw plugs and said bosses containing'a bore for re' ception of the wrist pin, and a. heat-transfer medium partially filling said pockets and sealed therein by said screw plugs.

WILLIAM HARPER, Jn. 

